Leaf structure and why it matters

Leaves exchange gases via stomata


CO2 IN, O2 and H2O OUT

How stomata work…


- CO2 enters leaf and then chloroplasts through concentration gradient
- Stomata are not always open….WHY???

Leaf gas exchange impacts the global atmopshere

Vascular tissues in leaves are confined to veins


  • Transpiration (leaf water loss) is a by‐product of opening stomatal pores

  • H2O transport needs to be sufficient to keep stomata open

  • Veins represents investment in H2O supply

Angiosperms have evolved higher vein densities

  • Helps explain angiosperm dominance
  • Transpiration alters global climate systems!

Leaf economic theory: Return on Investment

Photosynthesis is complicated….


What do plants do when they are hungry?

Photosynthesis is the basis for most life on Earth




  • Greek = “building with light”
  • Autotroph = “self nourishing”
  • Photoautotroph = “self nourishing with light”


  • Photosynthesis is an energy pathway
    • 2 linked reactions
    • light reaction + Calvin cycle

Chloroplasts: Where the magic happens

The nature of light


When light hits chlorophyll a few things can happen

When pigments absorb photons an election gets excited

Photosystems (2) convert light energy to chemical energy

Light reactions: make ATP + NADPH for Calvin cycle


Calvin cycle occurs in the stroma

Calvin cycle is a 3-step process

  • 1. Fixation: CO2 reacts with 5C molecule (RUBP)
    • new 6C split into 2 acids (3C each)
    • catalyzed by Rubisco enzyme


  • 2. Reduction: ATP and NADPH turn 3C acids into sugars
    • reduction of acids (requires electron carrier)
    • requires energy


  • 3. Regeneration: Some 3C sugars recycled to make RUBP (5C)
    • one 3C sugar leaves to make carbohydrates/sugars
    • recycling step also needs ATP

Making sugars requires several cycles